1. Field of the Invention
This invention relates to a method of recognizing the shape of a road which can be used by, for example, a system provided on a vehicle. In addition, this invention relates to an apparatus for recognizing the shape of a road which can be used by, for example, a system provided on a vehicle. Furthermore, this invention relates to a recording medium which stores a computer program for recognizing the shape of a road.
2. Description of the Related Art
A known obstacle detecting apparatus for a vehicle emits a forward wave beam such as a light beam or a millimeter wave beam from the body of the vehicle, and controls the forward wave beam to periodically scan a given angular region in front of the body of the vehicle. In the case where an obstacle exists in the given angular region, the forward wave beam encounters the obstacle before being at least partially reflected thereby. A portion of the reflected wave beam returns to the apparatus as an echo wave beam. The apparatus detects the obstacle in response to the echo wave beam.
The known obstacle detecting apparatus is used in a warning system for a vehicle which alarms when an obstacle such as a preceding vehicle exists in a given angular region in front of the present vehicle. The known obstacle detecting apparatus is used also in a system for a vehicle which controls the speed of the vehicle to maintain a proper distance between the vehicle and a preceding vehicle.
The known obstacle detecting apparatus additionally has the function of determining whether or not the detected obstacle is a preceding vehicle. In general, this determination is responsive to the output signals from a steering angle sensor and a yaw rate sensor. In the case where the present vehicle is traveling along a straight portion of a road while a preceding vehicle is traveling along a curved road portion extending ahead of the straight road portion, the known obstacle detecting apparatus has a chance of erroneously determining the preceding vehicle.
In view of such a problem in the known obstacle detecting apparatus, it is proposed to recognize the shape of a road from objects on the sides of the road such as delineators. When there is a plurality of sensed delineators, a road edge or edges can be detected from the sensed delineators. On the other hand, when there is only one sensed delineator, a road edge can not be detected.
Japanese patent application publication number 8-249598 discloses an apparatus for sensing delineators and recognizing a road shape from information about the sensed delineators. According to Japanese application 8-249598, in the case where only one sensed delineator exists, a road shape is recognized from the trajectory or locus of the delineator which reflects relative motion between the present vehicle and the delineator. When the present vehicle is traveling along a curved road with a constant radius of curvature, it is possible to accurately recognize the road shape from the trajectory of the delineator. The accurate recognition of the road shape provides accurate detection of a preceding vehicle. On the other hand, when the present vehicle is traveling along a curved road with a varying radius of curvature, the shape of a road portion extending ahead of the sensed delineator can not be accurately recognized from the delineator trajectory.
Japanese patent application publication number 10-239436 discloses an apparatus for detecting the vehicle-to-vehicle distance. The apparatus in Japanese application 10-239436 emits a forward laser beam, and controls the forward laser beam to periodically scan a given angular region in front of the body of the present vehicle. The apparatus in Japanese application 10-239436 detects objects in the given angular range from return laser beams coming therefrom. Specifically, the apparatus detects the distances to the objects and the directions (the angular positions) of the objects relative to the present vehicle. The detected objects include reflectors on the right-hand and left-hand sides of a road. In the apparatus of Japanese application 10-239436, the shape of the road is recognized from the loci (trajectories) of detected reflectors on the road sides. The apparatus of Japanese application 10-239436 has a problem similar to that in the apparatus of Japanese application 8-249598.
It is a first object of this invention to provide a method of accurately recognizing the shape of a road even when only one sensed delineator exists.
It is a second object of this invention to provide an apparatus for accurately recognizing the shape of a road even when only one sensed delineator exists.
It is a third object of this invention to provide a recording medium which stores a computer program for accurately recognizing the shape of a road even when only one sensed delineator exists.
A first aspect of this invention provides a method of applying a transmission wave to a predetermined angular range in a width-wise direction of a vehicle, and recognizing a shape of a road extending ahead of the vehicle on the basis of a reflected wave which results from reflection of the transmission wave. The method comprises the steps of detecting a position of each object and a relative speed of the object on the basis of the reflected wave; determining whether each object is moving or stationary on the basis of the detected relative speed of the object and a speed of the vehicle; for at least one of right-hand and left-hand sides of the vehicle, calculating and memorizing a vehicle width-wise direction position where each stationary object effective for road shape recognition passes through the related side of the vehicle on the basis of the detected position of the object and a result of determining whether the object is moving or stationary; and recognizing a line connecting the memorized vehicle width-wise direction position and the detected position of the currently handled object corresponding to the effective stationary object as a road edge.
A second aspect of this invention is based on the first aspect thereof, and provides a method further comprising the steps of calculating and memorizing an average vehicle width-wise direction position among the calculated vehicle width-wise direction positions; and using the average vehicle width-wise direction position in the road edge recognition.
A third aspect of this invention provides an apparatus for recognizing a road shape. The apparatus comprises radar means for applying a transmission wave to a predetermined angular range in a width-wise direction of a vehicle, and detecting a position of each object on the basis of a reflected wave which results from reflection of the transmission wave; and recognizing means for recognizing a shape of a road extending ahead of the vehicle on the basis of a result of detection by the radar means. The recognizing means comprises 1) object recognizing means for detecting a position of each object and a relative speed of the object on the basis of the result of detection by the radar means, and for determining whether the object is moving or stationary on the basis of the detected relative speed of the object and a speed of the vehicle; 2) position calculating and memorizing means for, regarding at least one of right-hand and left-hand sides of the vehicle, calculating and memorizing a vehicle width-wise direction position where each stationary object effective for road shape recognition passes through the related side of the vehicle on the basis of a result of function by the object recognizing means; 3) correspondence determining means for determining whether or not an object currently handled by the object recognizing means corresponds to the vehicle width-wise direction position memorized by the position calculating and memorizing means; and 4) road edge recognizing means for, in cases where the correspondence determining means determines that the object currently handled by the object recognizing means corresponds to the vehicle width-wise direction position, recognizing a line connecting the vehicle width-wise direction position and the detected position of the object currently handled by the object recognizing means as a road edge.
A fourth aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the position calculating and memorizing means comprises means for calculating and memorizing an average among vehicle width-wise direction positions for effective stationary objects, wherein the correspondence determining means comprises means for using the average as the vehicle width-wise direction position, and wherein the road edge recognizing means comprises means for using the average as the vehicle width-wise direction position.
A fifth aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the position calculating and memorizing means comprises means for calculating and memorizing a vehicle width-wise direction position or an average position for the right-hand side of the vehicle, and means for calculating and memorizing a vehicle width-wise direction position or an average position for the left-hand side of the vehicle, wherein the correspondence determining means comprises means for determining whether or not a currently handled object corresponds to the vehicle width-wise direction position or the average position for the right-hand side of the vehicle, and means for determining whether or not a currently-handled object corresponds to the vehicle width-wise direction position or the average position for the left-hand side of the vehicle, and wherein the road edge recognizing means comprises means for recognizing right-hand and left-hand road edges on the basis of the vehicle width-wise direction positions or the average positions for the right-hand and left-hand sides of the vehicle and a result of function by the correspondence determining means.
A sixth aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the road edge recognizing means comprises means for, in cases where there are a plurality of objects determined to correspond to the vehicle width-wise direction position, implementing interpolation with respect to regions between the objects to form lines connecting the objects and recognizing the lines connecting the objects and a line connecting the vehicle width-wise direction position and the detected position of nearest one of the objects as a road edge.
A seventh aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the position calculating and memorizing means comprises means for calculating a circle whose tangent vector is equal to a relative speed vector of the effective stationary object, and whose center is on a vehicle width-wise direction, and means for using a point of intersection between the circle and the vehicle width-wise direction as the vehicle width-wise direction position.
An eighth aspect of this invention is based on the fourth aspect thereof, and provides an apparatus wherein the position calculating and memorizing means comprises means for calculating a first average among vehicle width-wise direction positions through a simple mean process, means for disregarding each vehicle width-wise direction position which differs from the first average by at least a predetermined value, means for, in cases where the number of the vehicle width-wise direction positions except the disregarded positions is equal to or greater than a predetermined number, calculating a second average among the vehicle width-wise direction positions except the disregarded positions and using the second average as the final average, and means for, in cases where the number of the vehicle width-wise direction positions except the disregarded positions is smaller than the predetermined number, determining that the calculation of the final average is impossible.
A ninth aspect of this invention is based on the third aspect thereof, and provides an apparatus wherein the correspondence determining means comprises means for setting an object as an object to be determined which satisfies execution allowance conditions such that the object is stationary and a distance to the object is equal to or less than a predetermined value, and means for, in cases where an absolute value of a difference between a vehicle width-wise direction position of the determination object and the vehicle width-wise direction position memorized by the position calculating and memorizing means is smaller than a predetermined value, determining that the determination object and the vehicle width-wise direction position correspond to each other.
A tenth aspect of this invention is based on the ninth aspect thereof, and provides an apparatus wherein the predetermined value in the execution allowance conditions which occurs in the presence of a chance that the vehicle changes lane is smaller than that occurring in the absence of the chance.
An eleventh aspect of this invention is based on the third aspect thereof, and provides an apparatus further comprising erroneous correspondence determining means for, regarding the object which is determined by the correspondence determining means to correspond to the vehicle width-wise direction position, determining whether or not an object on the opposite road side is erroneously determined to correspond to the vehicle width-wise direction position while considering conditions of a curvature of a road which occur during a predetermined time interval past, and for, when it is determined that an object on the opposite road side is erroneously determined to correspond to the vehicle width-wise direction position, correcting the determination and newly determining that the object does not correspond to the vehicle width-wise direction position and causing the object to be unused by the road edge recognizing means.
A twelfth aspect of this invention is based on the eleventh aspect thereof, and provides an apparatus wherein the erroneous correspondence determining means comprises means for calculating a circle whose tangent vector is equal to a relative speed vector of the effective stationary object, and whose center is on a vehicle width-wise direction, means for setting a radius of the circle as a curvature radius of a road, and means for, in cases where an absolute value of a difference between a vehicle width-wise direction position of the determination object which is predicted from a curvature radius available in a predetermined time interval past and the vehicle width-wise direction position memorized by the position calculating and memorizing means which corresponds to the opposite road side is smaller than a predetermined value, determining that the correspondence is erroneous.
A thirteenth aspect of this invention is based on the twelfth aspect thereof, and provides an apparatus wherein the erroneous correspondence determining means comprises means for, in cases where a stationary object on the opposite road side is not detected so that the vehicle width-wise direction position for the erroneous corresponding determination is unavailable, calculating a virtual vehicle width-wise direction position corresponding to the opposite road side on the basis of a road width and the vehicle width-wise direction position of the stationary object being the determination object, and using the virtual vehicle width-wise direction position in the erroneous correspondence determination.
A fourteenth aspect of this invention provides a recording medium storing a program for controlling a computer operating as the recognizing means in the apparatus of the third aspect of this invention.
A fifteenth aspect of this invention provides an apparatus for a vehicle which comprises first means for periodically detecting stationary objects in an area extending ahead of the vehicle; second means for calculating positions of the stationary objects detected by the first means relative to the vehicle; third means for calculating speeds of the stationary objects detected by the first means relative to the vehicle; fourth means for, from the positions calculated by the second means and the speeds calculated by the third means, predicting positions on a transverse axis with respect to the vehicle through which the stationary objects detected by the first means will pass as viewed from the vehicle; fifth means for selecting positions from among the positions predicted by the fourth means; sixth means for calculating an average position among the positions selected by the fifth means; seventh means for selecting at least one stationary object from among the stationary objects detected by the first means; and eighth means for recognizing a line connecting the average position calculated by the sixth means and the position of the stationary object selected by the seventh means as a road edge.